1. Field of the Invention
The present invention relates to the air conditioning and refrigeration arts and, more particularly, to a method of and to a system for measuring density of a liquid mixture in an enclosed flow air conditioning or refrigeration apparatus to determine the refrigerant/lubricant ratios of the liquid flowing therein.
2. Description of the Prior Art
A method and an apparatus disclosed in U.S. Pat. No. 4,522,068 to George E. Smith granted June 11, 1985 and entitled "Ultrasonic Densitometer for Liquid Slurries" utilizes the leading edge of a received compression wave resulting from a transmitted pulse into the liquid slurry whose density is being measured. A quantity of the liquid is isolated between a transmitting transducer and a receiving transducer, the two transducers being set at a predetermined distance from one another. Pulses at a predetermined ultrasonic frequency are used to drive the transmitting transducer. A latching output signal is produced with the development of each transmitted pulse and an unlatching output signal is produced with the receipt of the leading edge of the compression wave relating thereto as it is received by the receiving transducer. The time between the latching and the unlatching occurrences is determined, in digital fashion, using a high frequency counting scheme. The count is correlated against an empirically developed standard as an indication of the density of the slurry. On its face, the patent of Smith does not apply to determining refrigerant/lubricant ratios in enclosed flow air conditioning or refrigeration apparatus.
A method of and an apparatus for testing fluids is disclosed in U.S. Pat. No. 3,283,562 granted November 8, 1966 to Charles H. Heisig et al. and entitled "Fluid Testing by Wave Energy", wherein a limited portion of the wall of a liquid containing cavity is caused to vibrate mechanically in such fashion as to propagate acoustic wave energy in the liquid. Consequently, this acoustic wave energy is coupled, by a liquid, into the wall of the cavity to cause mechanical vibration thereof that represents some part of the original mechanical vibrations, but of a character determined, in part, by the acoustic properties of the liquid, variation in such properties modulating the acoustic wave energy propagated in the liquid. The vibrations in the wall, coupled thereto from the liquid, are sensed and demodulated in order to obtain information as to one or another of the acoustic properties, such as gas content in the form of a bubble or a plurality of bubbles or specks of gas, the gaseous component of liquid having a marked modulating effect on acoustic wave energy propagated in the liquid. No application is seen in using such techniques for the purpose of determining refrigerant/lubricant ratios in an enclosed flow air conditioning or refrigeration apparatus.
Refrigeration and air conditioning apparatus failure with few exceptions, is due to one of three conditions. These are leakage into or out of the apparatus, circulation malfunction and improper compressor lubricant oil conditions. The problems are especially significant in vehicle air conditioning systems, one such typical system being disclosed in U.S. Pat. No. 3,738,118 granted June 12, 1973 to James W. Jacobs and entitled "Means for Lubricating Vehicle Air Conditioning Compressor Shaft Seals". Of the above-mentioned three causes of malfunction or failure, the last, inadequate compressor lubrication, is the most frequent and most often the cause of catastrophic system malfunction. Refrigeration and air conditioning compressor lubrication is unique in that the refrigerant liquid mixes with the lubricating oil and creates lubrication hazards not commonly encountered in other classes of high speed rotating machinery.
The quantity of refrigerant in a typical apparatus may be greater than the quantity of lubricating crankcase oil in the apparatus compressor. Ordinarily, a portion of the crankcase oil is carried around the refrigeration system by the refrigerant. However, if too much oil leaves the compressor crankcase, or if too much oil is suddenly returned with the refrigerant to the compressor through the compressor inlet, failure of the compressor may result.
Should the liquid refrigerant replace the oil in the compressor crankcase during an inversion of the oil and refrigerant, which may occur with certain commonly used refrigerants when a sufficiently low crankcase temperature is attained, the oil in the compressor will be nearly completely swept out of the compressor and all lubricated interaction of the moving parts and bearing surfaces of the compressor will quickly be lost. Rapid catastrophic failure of the compressor and of the system results.
Moreover, the refrigerant used in many small refrigerating apparatus and in small air conditioning apparatus, such as in automobiles and the like, tends to leak out of the apparatus over periods of time, causing too much lubricant to be present in the circulating liquid, resulting in a reduced cooling capacity. When the refrigerant is replaced, one needs to take care so that the proper refrigerant/lubricant ratio range is achieved and is not exceeded.